The present invention relates to a fixing device applicable to an electrophotographic image forming apparatus such as a copying machine and a printer, and also relates to an image forming apparatus.
An electrophotographic image forming apparatus such as a copying machine and a printer may employ a pressure release member which presses a second fixing member (e.g. a pressure roller) against a first fixing member (e.g. a rotational fixing member such as a fixing roller and a fixing belt) by a biasing member with a predetermined pressing force, and which releases this pressure contact state where the second fixing member is pressed against the first fixing member with a predetermined pressing force.
As an example of the pressure release member, a fixing device disclosed in JP 2008-151965 A employs a cam having a large-diameter part and a small-diameter part. By utilizing the large-diameter part and the small-diameter part, this cam switches between a pressure contact state where a fixing roller (a first fixing member) and a pressure roller (a second fixing member) are pressed against each other and a released state where the pressure contact is released.
As another example of the pressure release member, a fixing device disclosed in JP 2003-223075 A employs a cam which abuts an end of a roller shaft of a pressure roller (a second fixing member) and which displaces the pressure roller in a direction away from a fixing roller (a first fixing member) against a biasing force of a spring.
As yet another example of the pressure release member, a fixing device disclosed in JP 2001-318555 A employs a cam by which a downward rotational movement of a release lever around a rotational shaft is converted into an upward rotational movement of a pressure lever around a first rotational shaft. By this converting action, the cam releases a pressure state where a pressure roller (a second fixing member) is pressed against a heating roller (a first fixing member).
In these conventional fixing devices, cams are used as the pressure release members for releasing the pressure contact state where the second fixing members are pressed against the first fixing members. However, this configuration requires a number of components for operating the pressure release members, and further requires a greater space and higher costs for such components.